This application is based upon application No. 2002-202750 filed in Japan, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a drive mechanism, a drive method and a circuit employed therein. More specifically, the present invention relates to the circuit suitable for applying a saw-tooth waveform of a voltage to a capacitive load, the drive mechanism provided with the circuit, and the drive method employing the circuit.
2. Description of the Related Arts
Conventionally, there have been two manners of running a drive mechanism in which a saw-tooth waveform of voltage is applied to a piezoelectric element.
Referring to FIGS. 1A through 1C, the first manner of running the drive mechanism will be explained. As shown in FIG. 1A, a waveform generator W, specifically a digital-analog transducer therein, for example, of 8 bits and 1-5 volts type, generates a voltage having a saw-tooth waveform. The voltage having the saw-tooth waveform is amplified, for example, up to 1-10 volts, by an amplifier M, and then is applied to a piezoelectric element X in order to running the drive mechanism. By adjusting the waveform generator W, a waveform of forward direction as shown in FIG. 1B and a waveform of backward direction as shown in FIG. 2C can be generated.
FIGS. 2, 3A and 3B show a second manner of running the drive mechanism. FIG. 2 shows a circuit for applying a power-supply voltage V to a piezoelectric element X. The circuit includes constant current circuits A, D and switching circuits B, C. The waveform of forward direction or the waveform of backward direction are generated by actuating the constant current circuit A and the switching circuit B alternately, or by actuating the constant current circuit D and the switching circuit C alternately.
For example, the circuit is constituted as shown in FIG. 3A. When control signals are input to terminals xe2x80x9caxe2x80x9d, xe2x80x9cbxe2x80x9d, xe2x80x9ccxe2x80x9d and xe2x80x9cdxe2x80x9d of the circuit, the waveform of forward direction or the waveform of backward direction is generated, as shown in FIG. 3B.
Specifically, when the terminal xe2x80x9caxe2x80x9d is supplied with Hi input, the voltage applied to a piezoelectric element X gradually increases through the constant current circuit A as shown by the reference numeral 10 in FIG. 3B. Next, when the terminal xe2x80x9cbxe2x80x9d is supplied with Hi input, the piezoelectric element X is grounded through the switch circuit B, so that the voltage applied to the piezoelectric element X rapidly decreases as shown by the reference numeral 12 in FIG. 3B. Thus, the waveform of forward direction is generated.
In the mean time, when the terminal xe2x80x9ccxe2x80x9d is supplied with Hi input, the piezoelectric element X is connected to the power supply voltage V through the switch circuit C, so that the voltage applied to the piezoelectric element X rapidly increases as shown by the reference numeral 14 in FIG. 3B. Then, when the terminal xe2x80x9cdxe2x80x9d is supplied with Hi input, the voltage applied to the piezoelectric element X gradually decreases through the constant current circuit D as shown by the reference numeral 16 in FIG. 3B. Therefore, the waveform of backward direction is generated.
In the first manner, the waveform generator W and the power amplifier M are needed. In the second manner, the constant current circuits A, D and the switch circuits B, C are needed. Thus, the construction of the circuit is complex and introduces high cost. Additionally, the waveform includes high-order harmonic waves, which are not needed, and causes undesirable influence upon the drive mechanism.
Accordingly, it is an object of the present invention to provide a drive mechanism, a drive method and a circuit employing a simple construction, in which a voltage having a saw-tooth waveform to be applied can be generated.
In order to achieve the above object, according to one aspect of the present invention, there is provided a drive mechanism, comprising: an electromechanical transducer operating as a capacitor and having a pair of terminals; an inductive element operating as an inductor and having a pair of terminals; and a resistive element operating as a resistor and having a pair of terminals, wherein the electromechanical transducer, the inductive element and the resistive element are connected by terminals thereof in series so as to constitute a series resonance circuit, and wherein a voltage having a saw-tooth waveform applied to the electromechanical transducer causes the electromechanical transducer to expand at a first velocity and to contract at a second velocity, different from the first velocity.
In the configuration, the electromechanical transducer (for example, electrostatic actuator, piezoelectric transducer, electrostriction transducer, magnetostriction transducer, and so on) changes the electrical energy (for example, electric voltage, electric current, electric field, electric charge, static electricity, magnetic field) supplied thereto into the mechanical energy (for example, transformation or strain such as prolonging, compressing, expanding, contracting, bending, twisting).
In the configuration, the transfer function of the series resonance circuit, which is a serial RLC circuit, includes a second-order lag element, and therefore a suitable waveform of the voltage applied to the series resonance circuit causes the saw-tooth or slant waveform of the voltage applied to the electromechanical transducer.
According to the configuration, it is possible to make parts of the circuit for generating a voltage applied to the electromechanical transducer less than that of conventional drive mechanisms. Thus, the voltage having the saw-tooth waveform applied to the electromechanical transducer can be generated, employing a simple construction.
As an embodiment, a voltage having a square waveform applied to the series resonance circuit generates the voltage having the saw-tooth waveform applied to the electromechanical transducer.
In the configuration, it is easy to apply the voltage having the square waveform so as to generate the voltage having the saw-tooth waveform applied to the electromechanical transducer.
As an embodiment, one of the terminals of the electromechanical transducer is connected to ground. The other of the terminals of the electromechanical transducer is connected to one of the terminals of the resistive element. The other of the terminals of the resistive element is connected to one of the terminals of the inductive element. The voltage having the square waveform applied to the other of the terminals of the inductive element generates the voltage having the saw-tooth waveform applied to the other of the terminals of the electromechanical transducer.
As an embodiment, an inequality of
0.4xc3x97fr less than fd less than 1.0xc3x97frxe2x80x83xe2x80x83(1)
is satisfied, where fd is a frequency of the voltage having the square waveform applied to the series resonance circuit, and where fr is a resonance frequency of the series resonance circuit.
Preferably, an inequality of
0.6xc3x97fr less than fd less than 0.8xc3x97frxe2x80x83xe2x80x83(2)
is satisfied.
As an embodiment, one of inequalities of
0.05 less than Du less than 0.48 and 0.52 less than Du less than 0.95xe2x80x83xe2x80x83(3)
is satisfied, where Du is a duty ratio of the voltage having the square waveform applied to the series resonance circuit.
Preferably, one of inequalities of
0.15 less than Du less than 0.40 and 0.60 less than Du less than 0.85xe2x80x83xe2x80x83(4)
is satisfied.
More preferably, one of inequalities of
0.25 less than Du less than 0.35 and 0.65 less than Du less than 0.75xe2x80x83xe2x80x83(5)
is satisfied.
As an embodiment, an inequality of
(1/15)xc3x97(L/C)1/2 less than R less than (L/C)1/2xe2x80x83xe2x80x83(6)
is satisfied, where C is a capacitance of the electromechanical transducer, where L is an inductance of the inductive element, and where R is a resistance of the resistive element.
Preferably, an inequality of
(1/10)xc3x97(L/C)1/2 less than R less than (1/1.5)xc3x97(L/C)1/2xe2x80x83xe2x80x83(7)
is satisfied.
As an embodiment, the electromechanical transducer has a pair of ends in an expanding and contracting direction. The drive mechanism further comprises a drive member fixed to one of the ends of the electromechanical transducer; and a driven member which contacts frictionally with the drive member under a predetermined frictional force exerting therebetween. The voltage having the saw-tooth waveform applied to the electromechanical transducer causes the electromechanical transducer to expand at the first velocity and to contract at the second velocity, different from the first velocity, so as to move the driven member along with the drive member relatively.
According to the above embodiments, it is possible to generate a suitable waveform of the voltage applied to the electromechanical transducer for running the drive mechanism.
In order to achieve the above object, according to another aspect of the present invention, there is provided a drive method for running a drive mechanism which comprises: an electromechanical transducer operating as a capacitor and having a pair of terminals; an inductive element operating as an inductor and having a pair of terminals; and a resistive element operating as a resistor and having a pair of terminals, wherein the electromechanical transducer, the inductive element and the resistive element are connected by terminals thereof in series so as to constitute a series resonance circuit, the driving method comprising: a first step of applying a voltage to the series resonance circuit so as to generate a voltage having a saw-tooth waveform applied to the electromechanical transducer; and a second step of expanding the electromechanical transducer at a first velocity and contracting at a second velocity, different from the first velocity, by the voltage having the saw-tooth waveform applied to the electromechanical transducer generated at the first step.
In the configuration, the electromechanical transducer (for example, electrostatic actuator, piezoelectric transducer, electrostriction transducer, magnetostriction transducer, and so on) changes the electrical energy (for example, electric voltage, electric current, electric field, electric charge, static electricity, magnetic field) supplied thereto into the mechanical energy (for example, transformation or strain such as prolonging, compressing, expanding, contracting, bending, twisting).
In the configuration, the transfer function of the series resonance circuit, which is a serial RLC circuit, includes a second-order lag element, and therefore a suitable waveform of the voltage applied to the series resonance circuit causes the saw-tooth or slant waveform of the voltage applied to the electromechanical transducer.
According to the configuration, it is possible to make parts of the circuit for generating a voltage applied to the electromechanical transducer less than that of conventional drive mechanisms. Thus, the voltage having the saw-tooth waveform applied to the electromechanical transducer can be generated, employing a simple construction.
As an embodiment, the voltage having a square waveform is applied to the series resonance circuit to perform the first step.
In the configuration, it is easy to apply the voltage having the square waveform so as to generate the voltage having the saw-tooth waveform on the electromechanical transducer.
As an embodiment, one of the terminals of the electromechanical transducer is connected to ground. The other of the terminals of the electromechanical transducer is connected to one of the terminals of the resistive element. The other of the terminals of the resistive element is connected to one of the terminals of the inductive element. The voltage having the square waveform is applied to the other of the terminals of the inductive element so as to generate the voltage having the saw-tooth waveform applied to the other of the terminals of the electromechanical transducer to perform the first step.
As an embodiment, an inequality of
0.4xc3x97fr less than fd less than 1.0xc3x97frxe2x80x83xe2x80x83(1xe2x80x2)
is satisfied, where fd is a frequency of the voltage having the square waveform applied to the series resonance circuit, and where fr is a resonance frequency of the series resonance circuit.
Preferably, an inequality of
0.6xc3x97fr less than fd less than 0.8xc3x97frxe2x80x83xe2x80x83(2xe2x80x2)
is satisfied.
As an embodiment, one of inequalities of
0.05 less than Du less than 0.48 and 0.52 less than Du less than 0.95xe2x80x83xe2x80x83(3xe2x80x2)
is satisfied, where Du is a duty ratio of the voltage having the square waveform applied to the series resonance circuit.
Preferably, one of inequalities of
0.15 less than Du less than 0.40 and 0.60 less than Du less than 0.85xe2x80x83xe2x80x83(4xe2x80x2)
is satisfied.
More preferably, one of inequalities of
0.25 less than Du less than 0.35 and 0.65 less than Du less than 0.75xe2x80x83xe2x80x83(5xe2x80x2)
is satisfied.
As an embodiment, an inequality of
(1/15)xc3x97(L/C)1/2 less than R less than (L/C)1/2xe2x80x83xe2x80x83(6xe2x80x2)
is satisfied, where C is a capacitance of the electromechanical transducer, where L is an inductance of the inductive element, and where R is a resistance of the resistive element.
Preferably, an inequality of
(1/10 )xc3x97(L/C)1/2 less than R less than (1/1.5)xc3x97(L/C)1/2xe2x80x83xe2x80x83(7xe2x80x2)
is satisfied.
As an embodiment, the electromechanical transducer have a pair of ends in an expanding and contracting direction. The drive mechanism further comprises: a drive member fixed to one of the ends of the electromechanical transducer; and a driven member which contacts frictionally with the drive member under a predetermined frictional force exerting therebetween. The second step of expanding the electromechanical transducer at the first velocity and contracting at the second velocity, different from the first velocity, is carried out so as to move the driven member along with the drive member.
According to the above embodiments, it is possible to generate a suitable waveform of the voltage applied to the electromechanical transducer for running the drive mechanism.
In order to achieve the above object, according to still another aspect of the present invention, there is provided a circuit for generating a voltage having a saw-tooth waveform, comprising: an capacitance element operating as a capacitor and having a pair of terminals; an inductive element operating as an inductor and having a pair of terminals; and a resistive element operating as a resistor and having a pair of terminals, wherein the capacitance element, the inductive element and the resistive element are connected by terminals thereof in series so as to constitute a series resonance circuit, and wherein a voltage having a square waveform applied to the series resonance circuit generates the voltage having the saw-tooth waveform applied to the capacitance element.
In the configuration, the transfer function of the series resonance circuit, which is a serial RLC circuit, includes a second-order lag element, and therefore a suitable waveform of the voltage applied to the series resonance circuit generates the saw-tooth or slant waveform of the voltage applied to the capacitive element.
According to the configuration, it is possible to make parts of the circuit for generating a voltage applied to the capacitive element less than that of conventional drive mechanisms. Thus, the voltage having the saw-tooth waveform applied to the capacitive element can be generated, employing a simple construction.
As an embodiment, one of the terminals of the capacitance element is connected to ground. The other of the terminals of the capacitance element is connected to one of the terminals of the resistive element. The other of the terminals of the resistive element is connected to one of the terminals of the inductive element. The voltage having the square waveform applied to the other of the terminals of the inductive element generates the voltage having the saw-tooth waveform applied to the other of the terminals of the capacitance element.
As an embodiment, an inequality of
0.4xc3x97fr less than fd less than 1.0xc3x97frxe2x80x83xe2x80x83(1xe2x80x3)
is satisfied, where fd is a frequency of the voltage having the square waveform applied to the series resonance circuit, and where fr is a resonance frequency of the series resonance circuit.
Preferably, an inequality of
0.6xc3x97fr less than fd less than 0.8xc3x97frxe2x80x83xe2x80x83(2xe2x80x3)
is satisfied.
As an embodiment, one of inequalities of
0.05 less than Du less than 0.48 and 0.52 less than Du less than 0.95xe2x80x83xe2x80x83(3xe2x80x3)
is satisfied, where Du is a duty ratio of the voltage having the square waveform applied to the series resonance circuit.
Preferably, one of inequalities of
0.15 less than Du less than 0.40 and 0.60 less than Du less than 0.85xe2x80x83xe2x80x83(4xe2x80x3)
is satisfied.
More preferably, one of inequalities of
0.25 less than Du less than 0.35 and 0.65 less than Du less than 0.75xe2x80x83xe2x80x83(5xe2x80x3)
is satisfied.
As an embodiment, an inequality of
(1/15)xc3x97(L/C)1/2 less than R less than (L/C)1/2xe2x80x83xe2x80x83(6xe2x80x3)
is satisfied, where C is a capacitance of the electromechanical transducer, where L is an inductance of the inductive element, and where R is a resistance of the resistive element.
Preferably, an inequality of
(1/10)xc3x97(L/C)1/2 less than R less than (1/1.5)xc3x97(L/C)1/2xe2x80x83xe2x80x83(7xe2x80x3)
is satisfied.
According to the above embodiments, it is possible to generate a suitable waveform of the voltage applied to the capacitive element for actuating the capacitive element.